1. Field of the Invention
The present invention relates to improved fine particle size cementing compositions which can be utilized in general construction as well as in cementing wells.
2. Description of the Prior Art
In general cementing operations wherein hard substantially impermeable cementitious masses are formed in desired locations, hydraulic cement compositions have heretofore been utilized which contain relatively large particle size hydraulic cements, e.g., Portland cements, along with water and other additives.
In specialized cementing operations such as those carried out in constructing and repairing oil, gas and water wells, large particle size cement compositions have also been utilized. In primary well cementing, i.e., the forming of a cement sheath in the annular space between pipe disposed in a well bore and the walls of the well bore, a pumpable hydraulic cement composition is introduced into the annular space and the cement composition is permitted to set therein. The resulting cement sheath provides physical support and positioning to the pipe in the well bore and prevents unwanted fluid migration between subterranean zones and formations penetrated by the well bore.
After a well has been utilized in the recovery of fluids from or the introduction of fluids into subterranean formations, problems relating to the undesirable passage of fluids into and from subterranean formations or the well bore penetrating such formations sometimes occur. This undesirable passage of fluids ordinarily involves the flow of oil, gas or water through small openings such as holes or cracks in well casings; holes, cracks, voids or channels in the cement sheath in the annular space between the walls of the well bore and the pipe therein; very small spaces between the cement sheath and the exterior surface of the casing or the walls of the well bore; and permeable spaces in gravel packs and formations. Heretofore, such openings have been plugged or attempted to be plugged using cement compositions of relatively large particle size. As a result, when the openings are very small, it is difficult to cause the cement composition of relatively large particle size to enter the openings and set therein whereby the openings are plugged. If the cement composition utilized cannot enter the openings, at best a bridge or patch may be formed over the openings to produce only a temporary termination of the undesirable fluid flow.
Recently, fine particle size cement compositions have been used successfully in the construction and repair of wells. Such fine particle size cement compositions and methods of their use are described in detail, for example, in U.S. Pat. Nos. 5,086,850 entitled Squeeze Cementing issued Jun. 16, 1992 and No. 5,125,455 entitled Primary Cementing issued on Jun. 30, 1992. Because of the fine particle size of the cement, the cement compositions can readily be forced into and through very small openings, they can have low densities and they quickly develop gel strength after placement. However, fine particle size Portland and other cements are expensive, and the cement compositions utilizing such cements have often suffered from poor compressive strength development at low temperatures.
A variety of drilling fluids are used in drilling wells. Generally, the drilling fluids are solids containing water base gels or hydrocarbon based fluids which can be non-weighted or weighted with particulate weighting materials such as barite. After a well bore is drilled, during which the drilling fluid used is circulated through the well bore, circulation of the drilling fluid is stopped while the well is logged and pipe is run in the well bore. The drilling fluid in the well bore is then conditioned by circulating drilling fluid downwardly through the interior of the pipe and upwardly through the annulus between the exterior of the pipe and the walls of the well bore while drilling solids and gas are removed therefrom. Primary cementing operations are then performed in the well bore, i.e., the pipe disposed in the well bore is cemented therein by placing a cement composition in the annulus between the pipe and the walls of the well bore. When the cement composition is pumped down the pipe and into the annulus, the drilling fluid in the pipe and the annulus is displaced therefrom. The used drilling fluid is generally accumulated in a pit or tank and then disposed of.
The disposal of drilling fluid is time consuming and expensive, particularly in offshore drilling locations, and the drilling fluid often must be disposed of as a fluid which is hazardous to the environment. Thus, any environmentally safe use to which all or part of the drilling fluid can be put at the well site is highly advantageous in that it eliminates the need for disposal of the drilling fluid so used.
There remains a need in cementing applications, and particularly in the construction and repair of oil, gas and water wells for fine particle size cementing compositions and methods wherein the compositions are relatively inexpensive and have good compressive strength development at low temperatures. In addition, there is a need for such fine particle size cementing compositions and methods wherein the compositions can contain drilling fluid. That is, there is a need for cementing compositions and methods wherein portions of the drilling fluids used to drill wells can be utilized as components in the cementing compositions used for carrying out cementing operations in the wells, e.g., primary cementing operations. The portions of the drilling fluids which are not utilized in the cementing operations can be disposed of by combining them with the cementing compositions and forming the resulting cementing composition-drilling fluid mixtures into hard environmentally safe cementitious masses in underground or other locations.